No they where taking Clenbuterol or DNP which will make anyone lose weight like no tomorrow no mater their activity level. For a significant cost that is.
The more disturbing thing is male actors are clearly taking PEDs and/or being dehydrated for shirtless shots, distorting what a normal body should look like. Even in fitness circles where I live, no one looks that good without juicing or prepping their body for the shirtless pic.
[0] https://www.nydailynews.com/life-style/hollywood-dirty-diet-...